PHANEROGAMIA 



517 



part in the formation of the lower end of the embryo. The segmentation of 

 the embryo presents differences according to whether the plant belongs to the 

 Monocotyledons or Dicotyledons. IN THE LATTI.U TWO COTYLEDONS ARE FORMED 

 AT THE END OF THE GROWING EMBRYO (FlG. 505), AND THE GROWING POINT OF 

 THE SHOOT ORIGINATES AT THE BASE OF THE DEPRESSION BETWEEN THEM. 

 MONOCOTYLEDONS, ON THE OTHER HAND, HAVE A SINGLE LARGE TERMINAL 

 COTYLEDON, THE GROWING POINT BEING SITUATED LATERALLY (Fig. 506). 

 In both cases the root is formed from the end of the embryo which is directed 

 towards the micropyle ; its limits can bo readily traced in older embryos, and it 



I . 508. Fertilisation <>{ Ulinni Martagon. 

 One of the male nuclei is close to the 

 nucleus of tin' ovum, the other is in con- 

 tact with the nuclei of the embryo-sac. 

 (After GncXARD.) 



Fl<;. .">04. -.1, Kmlii vo-sar of lli-lin ntli .< mi n u >.'x 

 (alter NAWASCHIN). H. The male nuclei more 

 highly magnified. ;>x, iiolli-n-tulie ; ,vj, &,, 

 vvnerjji'lse ; </>[, .-'/'>. male nuclei ; 

 cell ; ek. nucleus of embryo-sac ; . antipodal 

 cells. 



can be seen that a few cells are derived from the hypophysis adjoining the 

 embryonic cell. 



The physiological significance of the phenomenon of APOGAMY ( na ), which has 

 recently been accurately investigated in several Angiosperms, has already been 

 considered (p. 302). Thorough investigation of the embryology has shown that in 

 these cases we have to do with apogamy and not, as was first assumed, with 

 parthenogenesis. The reduction in number of the chromosomes (p. 84) is omitted 

 in the development of the embryo-sac-, all the nuclei of which have the vegetative 

 number of chromosomes ; they are vegetative nuclei, not generative, and the egg- 

 cell is apogamous and not parthenogenetic. The fact that the loss of sexuality 

 is particularly shown in polymorphic genera such as Alchcmilla, Hierncium, 



